Implicit diversity combining based on the EM algorithm for fading channels with correlated path components

An iterative pilot symbol aided procedure for detection in multipath fading channels that does not neglect intersymbol interference (ISI) and achieves diversity combining with unresolved signal path components is introduced. The algorithm resolves the received signal into components corresponding to each path. The estimated components are combined for obtaining the next sequence estimate, and, thus, no signal energy is lost. The proposed approach attempts iterative unconstrained maximization of the likelihood function using the expectation-maximization (EM) algorithm. The EM solution is based on the approach to parameter estimation for superimposed signals introduced by Feder and Weinstein (1988). It allows for symbol-by-symbol maximization in the M-step for orthogonal signaling pulses.